Electrical control apparatus



ept. 19, 196 J. F. REUTHER ETAI. 3,001,123

ELECTRICAL CONTROL APPARATUS Filed June 25, 1959 2 Sheets-Sheet 1 Fig.2

Fig.l

d n m n I 4 Mum N hH R E g vmo o n 26 w 7% Cl n hm? 00 I JJ Net Control Ampere-turns \LLFIIIFI 153? m i. QC Ni Sept. 19, 1961 J. F. REUTHER ETAL 3,001,123

ELECTRICAL CONTROL APPARATUS 2 Sheets-Sheet 2 Filed June 25, 1959 3,001,123 ELECTRICAL CONTROL APPARATUS John F. Reuther, Penn Hills Township, Allegheny County,

and James T. Carleton, Forest Hills Borough, Pa., as-

signors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed June 25, 1959, Ser. No. 822,806 22 Claims. (Cl. 322--25) This invention relates to electrical control apparatus and more particularly to auctioneering circuits used in electrical control apparatus, such as regulator systems.

In certain types of electrical control apparatus, such as the type which includes magnetic amplifiers, it is sometimes necessary to provide an auctioneering or control circuit in which the output is responsive to or varies with only the larger or the smaller of two input control signals. In conventional control or auctioneering circuits of the latter type, the comparison of the two input control signals is usually accomplished on the basis of the relative'voltages of said control signals. In certain applications, the latter conventional method of comparing voltage of two control signals has certain disadvantages. For example, the difierence between the voltages of the control signals may be so great that it is necessary to introduce additional amplification for one of the control signals before comparing their voltages. In addition, the introduction of additional amplification in certain types of electrical control apparatus, such as regulator systems, adversely alfects the stability of the overall control apparatus. It is therefore desirable to provide an improved control of auctioneering circuit in which the output varies only with the larger or the smaller of two input control signals and in which the. comparison of the control signals is accomplished on a current basis, rather than on a'voltage basis.

It is an object of this invention ,to provide anew and improved electrical control apparatus for: obtaining an output which varies only with the larger of two input controlsignals.

Another object of this invention is to providean improved auctioneering circuit for obtaining an output which varies only with the larger of two input control currents.

A further object of the invention is to provide a new and improved limit circuit for use in electrical control apparatus, such as regulator systems.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a schematic diagram of one embodiment of our invention;

FIG. 2 is a partial schematic diagram of a second embodiment of our invention i FIG. 3. is a schematic diagram of a third embodiment of our invention; and w FIG. 4 is a graph illustrating the transfer curve of the magnetic amplifier shown in FIG. 3.

In general, the control or auctioneering circuit shown in FIG. 1 comprises a magnetic amplifier 60 and rectifier means including the rectifiers 92 and 96 which are connected in circuit relationship between a source of alternating current voltage 36 and a load circuit including a load 3,001,123 Patented Sept. 19, 1961 ice amplifier 60 comprises two magnetic core members 124 and 126. In this instance, the load windings 32 and 34 aredisposed in inductive relationship with the magnetic core members 124- and 126, respectively. As is customary, self-saturation for the magnetic amplifier 60 is obtained by connecting in series circuit relationship with the load windings 32 and 34, the self-saturating rectifiers 62 and 64, respectively. In order to form a doubler circuit of the magnetic amplifier 60, the series circuit including the load winding 32 and the self-saturating rectifier 62 is connected in parallel circuit relationship with the series circuit including the load winding 34 and the self-saturating rectifier 64.

Energy for the load windings 32 and 34 of the magnetic amplifier 60 is received from a transformer 70 having a primary winding 84, which in this instance is responsive to the output voltage of the alternating current source 36, and a secondary winding 82.

the hereinbefore described parallel circuit of the mag netic amplifier 60 and with the secondary winding 82 of the transformer 70 in order to produce a direct-cur.-

' rent output for the magnetic amplifier 60 at the output for applying to said load anoutputsignal or voltage terminals and 112 which are connected to a load circuit which includes the load 100.

For the purpose of biasing the magnetic amplifier 60 by a predetermined amount, the bias windings 76 and 78 are disposed in inductive relationship with the magnetic core members 124 and 126, respectively. In particular, the bias windings 76 and '78 are connected in series circuit relationship with one another, the series circuit being connected through an adjusting rheostat 86 to the conductors 102 and 104 which have applied thereto a substantially constant direct-current voltage. In operation, the current flow through the bias windings '76 and 78 produces a magnetomotive force or ampere-turns with respect to their respective magnetic core members that opposes the magnetomotive force or ampere-turns produced by the current flow through the load windings 32 and 34, respectively. I

In order to render the magnetic amplifier 60 responsive to the first unidirectional or direct-current input control signal or current 1 from the first signal source 40 at the input terminals 42 and 44, a first set of control windings 46 and 48 is disposed in inductive relationship with the magnetic core members 124- and 126, respectively. In particular, the first control windings 46 and 43' are connected in series circuit relationship with one another, the series circuit being connected between the input terminal 42 of the first signal source 40 and the upper input terminal 101 of the rectifier means 96.

In order to render the magnetic amplifier 60 responsive to the second unidirectional or direct-current input control signal or current 1 from the second signal source 50 at the input terminals 52 and 54, a second set of control windings 56 and 58 is disposed in inductive relationship with the magnetic core members 124 and 126, respectively. In particular, the second control windings 56 and 58 are connected in series circuit relationship with one another, the series circuit being connected between the input terminal 52 of the second signal source 50 and the upper input terminal 101 of the rectifier means 96. It is to be noted that the first set of control windings 46 and 48 is connected in series circuit relationship with the second set of control windings 56 and 58 between the input terminal 42 of the first signal source 40 and the input terminal 52 of the second signal source 50 with the common terminal between said first and second sets of control windings being the upper inputterminal 101 of the rectifier means 96. The lower input terminal 44 of the first signal source 40 and the lower input ter- As illustrated, a full wave dry-type load rectifier 92 is interconnected with which will be explained hereinafter. 1

'The first control windings 46and 43 or the magn tic amplifier '60 are "so dis'po's'ed on'their respective magnetic core members 124: and 126that when the first input "con 'trolsignal or current Ii" from the'firstsignal'source 40 flows therethrough in-the direction indicatedin 1; a 'rnagnetom'otive force is produced-in the respective "mag;

neticc'o'rvmembe'r's, that'is additive with respect to-"the' magnetomotive 'forceor ampere-turns produced by the current flow'through the respective load windings 32 and 34,.as also "indicated in FIG. 1; Similarly, the second control windings 56 and 58 of the magnetic-amplifier 60 are so disposed on their respective magnetic corernenv bers 124 and 126 that when the secondinput; control signal or current I from the second signal source 50 flows therethrough in the direction indicated in FIG. 1,"a magnetom'otive force" is produced inflthe respective magnetic core members that is also additive with respect tothe magnetomotive force oram'pe're-tu-rns produced bythe currentfiow" through the respectivefload windings 32 n 1 t. I H i. If his assumed 'a's'a reference direction, that the directraitor an'in'put control signal or current ispositive when the ampere-turns or rnagnetomotive' force produced by the flo'w of said input si nal or current inithe'associated control windings is additive with respect to the magneto motive force or ampere' turnsproduced by' the flow of current through. the respective load'windings'SZ and 34 thus tending to drivethe magnetic core members124' and 126 towards"saturation and increasing the output signal of the magnetic amplifier 60, then the directions of the first and second inputcontrol signals or currents '1 and I respectivelyg'would bothbe positive with re'-' spect tothe assumed'reference direction. On the other I hand, 'if'the directions of the input 'controlsignals "or currents applied to the first control windings 46' and 48 and to the se con d.controlwindings 56 and 58 were oppo site to the assumed reference direction, which would also be opposite in direction to the directions of the first and second input control signals or ct'lrrents l andI yrespcctively, shown in FIG. 1, then the direction of such input control signals ofcilrrents would be negative with'respe ct to the assumed reference direction .t-hus tending to drive the magnetic core members 124 and 126 away from satu'ra'tion decreasing the output signal of the mag netic amplifier60 p In' order to'rende'r the'magnetic amplifier 60' responsive to the absolute magnitude of the algebraic=dilference between the first and second input control"signalsor-currents I and I ,'""respectively,a third set of control windings 72 and 74 is disposed'in inductive relationship with ,the magnetic core members 124 and 126, respectively. In

particular, theth'ird' control windings 72 and 74 are connected in ser'iescir'cuit relationship with eachother, the series circuit beingconnectedthrough 'aresistor 88' across a the output terminals 105 and 107 of'the full-wave; bridge type rectifie'ri96 whose input terminals areconnected-to V the common junction point between the first control of the' algebraic' difference between the first and second input control :signals 1 and I I respectively, the: direction of the "difference signal or current 1 being always in; a positive direction. withrespectto the. assumedz-reference "direction xpreviouslyxdiscussed because of the, manner; in

- third control windings 72 and 74. 1 w

The thind controlwindings 72 and 74 are so disposed on their respective magnetic core members-1:124 and 126 that when the dififerencesignal or current I flows therethrough in the direction indicated in FIG, 1, as determined by the full wave--rectifier-96, a=-firagnetombtive force" is produced in the respective magnetic core-Therm bers that is, additive with respect'to-the niagnetomotive force 7 or ampere-turns produced by the-current flow throughthe-respectiye load windings 32--and34i -For reasons which- ,will be discussed-hereinafter, the-number of turns in the third-control -windings72 -and-"74- issub stantially equal to the number of turns in the first control windings-=46and' 48 and to the-number of tlirns inthe second control windings 56 and 58;

- 'In-theoperation' of the control or auctioneering circuit shown-in FIG. 1, theoutput signal of voltage of the-magnetic amplifier 60- which appears "at the output ;-terminals 110 and'1'1 2 is responsive to or varies'vw'th' the algebraic sum or net total of the amperetum's or "magnetomotive forces-produced by the flowof-the first and second inpht wntrol signals or currents'h nd 1 respectivelyyin the first control'windings'46-and 48-ancl in-thesecondcdttwhichi-thetull-gwave rectifier 96 isiconnected in circuit relation -withtthe control 'windings of v the magne tic amrtrol windings "56 and 58, respectively,*and bythe 'fio'wo t the difference signal or current l ji'n-the third con-trol windings 72' and 74. 'The sum or net totalof the ampere= turnsiproduoed by the how of control signals or currents in the first, second. and third control windings-of the-mag netic' amplifier 60in turn varies with or {is responsiveto only the algebraically larger ofthe first and second input control signals '1 and 1 1: In other 'words -the' output oi' the magnetic amplifier 60 varies with'only the more posi tiye, with respect to the assumed reference direction previously'f mentioned; =01" less negativeof; the first -'and secon'd input control'signals -1 and-I respectively; a

For example, assuming that during operationyithe directions of the first and second input'controlsignals -or' currents I and I ;-respectively, are as shown'in FIG.-'land both are positive with respect-to the assumed refer'ence direction,,but that the magnitude of the first input com trol signal or currentl is algebraically larger or exceeds the magnitude of the second input control signal torcur rent I then a difference signalorcurrent l flwill fiowiin the direction indicated in-FIGL "1 from the -upper input terminal 101 of the rectifier 96 through one of; the recti through the'thirdc'ontrolwinding 72 and-74-to'-the term-i na1"'10 7 of the rectifier 96 and backto theotherinp'ut terminal 103 of the rectifier 96 -through as ectifienleg of the recti-fier"96; As mentioned previously-, therna'gnitude of the difference signal or current I will"be -egual to the absolutemagnitude of the algebraic diflt'erence between the first andsecond input control-signals=I -+and I ;--respectively. "Assuming that the number ofturns ijneach of the first, second and third control -windings of theiin'ag netic amplifier'60 is substantially equal to} N he algebraic sum ornet, total of-theampere-turns produced byl-the flow of the'respective control currentsinthe first, second and third control "windings "of the magnetie -ampl'fier 60 may be enpressedbythe'following equation:

c As shown by Eduatioh' 1; thesuni or net t' otal of the am- P 7c-turns produced by the flow ofthe respective control ler t in sin the t t s c d 1d irdrcontrvl condition is, substantially equalttp twice, the

vvindings of Y the magnetic amplifier 60"during"*the assume pe'i atin'g hirnsineachof said control windings times the algebraically larger assumed control signal or current I l":

n the other hand, assuming thatthe directions of the first and second input control .signals Land I respectively, are as shown in FIG, 1 and are both in'a positive direction'with respect to the assumed reference direction, but that the'magnitude of the second input controlcurrent or signal I is algebraically larger or exceeds the magnitude of the first input control signal or current 1 then a difference signal or current I .will flow from the lower input terminal 103 of the rectifier 96 through one of the rectifiers of the rectifier 96 to the terminal 105 and then to the third control windingsl z and '74; to the terminal 107 of the rectifier 96, and then to the upper input terminal 101 of the rectifier 96 through one of the rectifier legs of the rectifier 96. Because ofthe-operation of the rectifier means 96, the direction of the difference signal or current I is the same as previously discussed for the first assumed operating condition and the magnitude of said difference signal or current is again equal to the absolute, magnitude of the algebraic difference between the second input control signal I and 'the first input control signal or current I When the second input control sign-a1 I is algebraically larger 'or more positive than the first input control signal or current I the sum or net total of the ampere-turns produced by the flow of the re spective control currents in the first, second and third control windings of-the magnetic. amplifier 60 during the assumed operating condition maybe expressed bythe following equation: v i a 1' (2) NI +NI +N(I l '2NI As shown by Equation 2, the sum or net total of the ampere-turns produced by the flow of the respective control currents in the respective control windings of the magnetic amplifier ,60 'whenthesecond input control signal or current 1 is algebraically larger than the first input control signal or current 1 varies with or is responsive to twice the number of turns of each of said control windings times the algebraically larger second input control signal or current 1 v l In summary,.the output signal orv voltage of the magnetic amplifier 60 varieswith or is responsive to only the algebraically. larger or more positive with respect to assumed reference direction of the first and second input control signals or currents I and 1;, respectively. The latter operating characteristic of the control or auctioneering circuit shown in FIG. l'holds true even though one or both of the two input control signals or currents reverses with respect to an assumed reference direction, or becomes negative with respect to the latter assumed reference direction. Ifionly one of the two input control signals is negative with respect to the assumed reference direction, then the output of the magnetic amplifier 60will vary with only the more positiveof said input control signals. If both of the input control signals become negative with respect to the assumed reference direction, then the output of magnetic amplifier60 will vary with only the algebraically less negative of the two input control signals. It will be readily understood that the manner in which the third control windings 72 and 74 are disposed on the magnetic core members 124 and 126; respectively, of the magnetic amplifier 60 maybe readily modified or reversed in certain applications in order that the; output of the magnetic amplifier 60 in such applications will vary only with the algebraically smaller or more negative of two input control signals, that is, in accordance with the input control signal which iseither less positive or more negative. i 1

It is to be noted that the ampere-turns produced by the flow of the first and second input control signals 1 and I respectively, in the first control windings 46 and 48 and in the secondcontrol windings 56 and. 58, respectively, of the magnetic amplifier .60 takenwtogether varies with the algebraic sum of said first and second-input control signals or currents while the ampere-turns of the third control windings '72 and 7 4of -the magnetic amplifier 60 varies with the algebraic. diflerence between said first and "second input. control signals or currents. The summing of thelfirst' and second input control signals or currents l andfI respectively, is accomplished magnetically and is isolated electrically from the third control windings 72 and 74 in which the diiference between said input control signals is obtained by the use of the full wave rectifier means 96. j" I I t Referring now to FIG. 2, there is shown a control or auctioneering circuit illustrating a's-econd embodiment of the invention. The control or auctioneeringcircuit shown in FIG. 2 is similar "to'the auctioneering circuit shown in FIG. '1 except for the changes indicated bythe partial schematic diagram shown in FIG. 2. 'In particular, the control auctioneering circuit, shown in FIG. 2 is similar to the auctioneen'ng circuit shown in FIG. 1 that the full wave rectifier 96, the third control windings 72 and 74, the capacitor 94 and the resistor 88 are omitted firom the circuit shown in FIG. 1, and the windings, the rectifiers and the resistors shown in the partial schematic of FIG. 2 will be connected or substituted between the terminals 101 and 103as shown in FIG. 2. The'balance of the auctioneering circuit shown in FIG. 2 would be the same asfpreviously described for the auctioneering circuit of FIG. 1.

or current flows from the terminal 103: through therevIn general, the magnetic'amplifier 60' which is shown.

In order to render the magnetic amplifier-"60' respon sive to the difference signal or current when a first input control signal or current is algebraically larger than a second input control signal or current, the third control Wind'- ings 156 and 158- are disposed in inductive relationship with the magnetic core members 124 and 126 respectively. The third control windings 156 and 158 are connected in seriescircuit relationship ,with one another, the series circuit being connected between the terminal 101 through a first associated rectifier. 198 and the terminal 103 through a resistor 188. The third control windings 156 and 158 are so disposed .on the respective magnetic core members 124 and 126. that when a difierence signal or current flows from the terminal 101 through the rectifier 1-98 and the third control windings 156 and 158, the ampere-turns or magnetomotive force produced in the respective magnetic core members is additive with respect to the ampere-turns ormagnetomotiye force prowithone another, theseries circuit being connected between the terminal 101 through a second associated rectifier 196 and the terminal 103 through a resistor 186. The fourth control windings 166 and 168 of the magnetic amplifier 60' are so disposed on the respective magnetic core members 124 and 126 that when a difference signal sistor 188, the fourth control windings 166 and 1 68 and the rectifier 196 to the terminal 101 the ampere-turns or magnetomotive force produced in the respective core members thereby is additive with respect to the ampere- 7 turns ormagnetomotive force produced in the respective magnetic core members by the current flowin the "re-' spectiyelo ad windingsaof the magnetic amplifier 60f.

' In general; thebperation} offthe control ,QrT aucti-oneering circuit shown inFI G. 2 is'siirnlar to the operation of the current control or?'auctioneeriugicircuit' shown in FIG. 1'"as previously ,discusseil The number of windings-required inthe magnetic amplifier 60' is increa'sed isince a difference signal, ,on current flows in only' one? direction through each or the first and' vsecond 'rectifiers 196 and 19 8, respectively,.of the. auctioneering circuit shown in" 7 cordance vviththe more positive or less negative of'two input control signals or currents, as; previously described in ,detail forv the auctioneering circuit shown in FIG? .1; The circuit of- FIG.. Z-may be modified similarly to the v circuit of 'FIG. 1', 'as previously mentioned, to be responsive to an -"me" algebraicallysrnaller"ormore negative of two input control signals or currents. v

, Referring now to FIG..3, there is illustrated a dynamoelec'tricimachine, more specifically a' synchronous generatorv 210; having an excitation "field winding" 212 and the outputlte'rminals215,217 and 219. 'Infthis. instance, the generator 210; is di'sposed'to supply energy or'electric power to the lineconductors'21'4;216i and 218'which are part o-f'athre'e-phase electricallsystem or circuit. ,In'order to obtain an excitation voltage-across the'field windmg 212 of relatively larger magnitude; an exciter220 is provided: In this instance,"the excite r 220 comprises" an armature 222. which supplies currentto the field winding i212 offtheg'eneratjor 210, "a self-exciting field winding 224fand the buck. and boostexcitation fieldwinding226 and- 228, respectively,thejpurpose'of which 'willbe explained hereinafter." In order to maintain the output voltageiof the 'generator,10,' at substantially a-predetermined va1ue,.a regulator; loop or system 230, comprising an error detecting j circuit 3501501" obtaining an error signalor current which varies with the deviation of the output voltage of the'generator 210 fromiits-regu1ated value and a push-pull vmagnetic'i amplifier 240; is interconnected between itheioutput ofthe; generator-210 and the'bu'ck and boostfield'windings 226 and 228, respectively, of the excite'r 220..'." "1 it a A minimum excitation limit circuit 310 is connected to the'outputof the generator 10 for obtaining a-limiting signal which-varies with the stability limits of the gen- "erator 2.10 and cooperates with the push-pull'n agnetic amplifier. 240 of the regulator loop or system 230 to prevent the generator 210"from falling-"out of' step' or synchronism during certain operating-conditions;- In addition," an=auctioneeringcircuit comprising the' full wave rectifier 362rand the control-windings of the push-pull magneticamplifieriw,is connected in circuit relation "Wi ththe error detecting circuit 350 and the'minimum excitationlimit circuit 310 in order'that the net output of the magnetic'amplifien240; and-in turn'the'regulator system 23.0, respond toor vary only with the algebraicalit 'ly lar-ger of eitherthe error'signal from'the' error detecting circuit'350 or. thelimiting-signal from the minimum excitation limit circuit 310." I As hereinbe'fore mentionedythe I regulator loop 230 is provided in order tomaintain the magnitude of the" out- V Lput voltage of; the" generator 21'0 at-substantia]ly;a predetermined values? Foripurp'os'es' of clarity, the componentsmandf operation of therefg'ulator loop or system -wilLbe lidescribedlbefore' describing the Jjvari'ouscomponents and operation of the minimum excitation limit cir eratiori-ofthefegulator lobp230.

ln 'gene'ralr'theerror' detecting circuit 350 is connected in circuit relation with th'e output terminals 2l5, 2 17 and output signal or'current which varies with the deviation of-rtheoutput voltage "of" saidgenerator from a predetep mined; desired "re'gulated value: *In particular;the-error detecting circuit- 350 comprises a three-phasefull wave rectifier-326 and a'"constant potential orvoltagereference device 31 5 which produces at its output a substantially constant unidireetional or direct-current output woltages The -input*terminalsof the full-wave rectifier 326-are connected-acrossdhe secondary windings 324 of the potentialtransformers-32$=whoseprimary;windings 322 are connected across the output terminals 21552 17: and 219 of the generator 210'through the line oonductors214i 216 "and-21-8, respectivelyflo be responsive to ithe output voltage 1 of said generator. I Afilter circuit i including": a linear filter reactor 396 and a capacitor-398 is -intercon-i nected between-the outputiterminals' of thefull: wave c+ tifier -326--'and the terminals 345 and 346 in order produce a smooth direct current voltage across thegrslatter terminalswhich varies "with the-; output-=voltage of: i the generator 210. A- relatively high impedance, more spe cifically-the' resistor= 344,*is connected between the 'ter- -minal 345 and-the=termi na1 347 focprovid'ingat theoutput :eterinina-ls 346 and 347- of the error detectingfcircuit- 350 'Jan output signal ior current which; varies withazthe' output voltage of the generator 210. :In3order: to provide at the output terminals a td-and 347v of the error detecting circuit 350 an output sigilalior'current which remains substantially constant independently of variations the output voltage of the generator- P10 and-whichopposes the output signal or cur-rentof the. full wave rectifier 326;- the series circuit which includesthe-relatively high impediance more-specificallyvithe 'resis'tor 354 and the-'iconstant' potential or voltage reference device 315=is"connected between "the output terminals -=346 and 347 of theerror detecting circuit- 350. The net-*output signal or. icurr'ent of the error detecting circuit 350 which appears atsth'e output terminal 34mm -347 'is- 'the diiference qbetween ,the output signal's' or currents of the fullwave rectifier 326 and-the voltage reference device' 315 and: is -a= meas- V tire of the deviation of theoutput "voltage-of: the-agenerator 210 from the' predetermined idesirediiregulated value; The direction of the-unidirectional output signal orcurrent which appears at the output terminals; 346 and 347'ofthe e'rror detecting circuit 350 depends upon Whether the output signal or-currentifrom therfull wave rectifier 326 is -larger or-smaller than-the substantially constant unidirectional outputcurrent or signaltfrorn'zthe vol'tage'reference'device 315 1;; 11

As 'illustrated, theapush-pull magnetic amplifier: 240 comprises two main sections242 and-.244. xEaCh Of th sections 242 and :244-:ofthe {magnetic amplifienMU-is similarto the magnetic amplifier =60 or theauctioneering circuit shownin FIGt 1. The section 242 comprises two magnetic core members250-and252 andthevsection 244 comprises two magnetic core members-254 and 2 56.1 wI-n thisinstance,-theload windingsQSS; 260, 262 and Zed-tare disposedin inductive relationshipwith the magnetic were members 250, 252, 254 and'256;respectively. mAsris customary, self-saturation for theflmagnetic amplifier 240 isobtained bya connecting inl seriescircuit relationship withtheeloadwindingsa258, 260, 262'rand 264;:;the::se lfsaturating' rectifiers"266, 268,270 and 272, respectively. In order to' form; a doublercircuit; of the;.-section 242, the series circuit including the load windingv.-=258 and the self-saturating'rectifier266 is connected inlpar- I allel circuit relationship with the series circuit including theloadwinding 260 -21116 t-he -self saturating rectifiert 268.

' In -likemanner, in orderto form a doubler:circuit ofwthe section 244g-=the series' cir tit; including he lb imp 2 on 3:1; airs; l I

ad; winding ing the load winding 264 and the self-saturating rec'd-- Energy for the load windings 258,260, 262 and 264 of the magnetic amplifier 240 is received from a transformer 274 having a primary winding 276 which isY. re-:- sponsive to the output voltage of the generator 210 atthe line conductors-2 l4and 218 in this instance. As illustrated, a full wave dry type load rectifier 282 is interconnected with the hereinbefore described parallel circuit of the section 242 and with the secondary winding section 278 of the transformer 274 inorder to produce a unidirectional or direct-current output for the. section. 242 In like manner, a full wave, dry type loadrectifier 284 is interconnected with the hereinbefore described parallel circuit of the section 244 and with the secondary winding section 280 of the transformer 274 in order to obtain a unidirectional or direct-current'output for the section In this instance, the boost field, winding 1228 ofthe exciter 220 is responsive to the output of the loadrrecti fier 282 of the section 242 and the buck-fieldwinding 2260f the exciter 220 is responsiveto the output Ofjlhfi load rectifier 284 of the section 244; In operation, the buck ,field winding opposes the boost field; winding 2 2 8, In order. to provide means for changingthe gain inthe, regulator loop or system- 230, the variable resistors286 and 287 are connected in series circuit relationship with the boost field winding 228 and with the buck field winding 226,,respectively. 1 I

Forthe purpose of biasing each ofthese sections 242 and 244 of the magnetic amplifier 240 by a predetermined amount, the bias windings 290, 292,- 294 and296 are disposed in inductiverelationship with the magnetic ,core members 250, 252, 254 and 256,- respectively; In particular, the bias windings v290, 292, 294 and 296 are connected in series circuit relationship with one another, the series circuit being connected to the conductors 296 and 298 which have applied there-toa substantiallyi fcon stant; unidirectional or direct-current voltage. In operation, the current flow through the .bias, windings 290, 292, 29 4 and 296 produces ampere-turns ora rnagnetQ- motive force with respect to their respective magnetic core members that opposes the arnpere-turns'or, magneto motive force produced by the {current flow through the 'loadfwindings 258, 260,262 and 264, respectively; f i

,In' order to render the magnetic amplifier 2'40' responsive to the. output error signal or current froni'thef error detecting circuit 350, a first set of controlwindings 330,

332, 334 and336 is disposed in inductive relationship with the magnetic core members 250, 252, 25,4 and 256,

respectively. The, first control windings 330; 33g; 334

mag'fietomotiveforces'produced by the flow of the net error signal or current from the error detecting circuit 350 in the first control windings 330, 332, 334 and 336 of the magnetic amplifier 240 is indicated by the solid arrows in FIG. 3.

signal or current from the voltage reference device 315, the direction of the magnetomotive forces or ampereturns produced in their respective magnetic core members in the magnetic amplifier 240 by the flow of the net error or signal current from the error detecting circuit 350 in the first control windings 330, 332, 334 and 336 is indicated by the dotted arrows in FIG. 3. v

In order to render the magnetic amplifier 240 responsive to the limit signal from the minimum excitation limit circuit 310 during certain operating conditions, as will be explained in detail hereinafter, the limit windings or second control windings 314, 316, 318 and 320 are disposed in inductive relationship with the magnetic core members 250, 252, 254 and 256, respectively. The second control windings 314, 316, 318 and 320 are connected in series circuit relationship with one another, the series circuit being connected between the output terminal 365 of the minimum excitation, limit circuit 310 through a relatively high impedance, more specifically, the resistor 352, and theupper input terminal of the full wave rectifier3362.vv The lower input terminal of the full wave rectifier 362, which isconnected to the output terminal 346 of the error detecting circuit 350, is also connected to and 336 are connected in series circuit relationship with one another, the series circuit being connected between the output terminal 347 of the error detecting circuit 350 and the upper inputterminal of the. full'wave rectifier 362, whose purpose will be discussed hereinafter. lhe lower input terminal of the rectifier 362 is connected to the other output terminal 346 of the error detecting circuit 350. The first controlwindings 330, 332, 334mm 336 are so'disposed on their respective magnetic core .members .250, 252, 254,and' 256 that when current flows therethroughfthe magnetomotive force or ampere-turns produced thereby in the respective magnetic core inernbers opposes or is additive with respect to the magneto motive force or ampere turns produced by the 'curreht flow through the respective load windin g s '258, 260, 262 and 264 depending upon" whether "the output currentjjof the fullwave rectifier ,326 is larger or smaller thant-he' output current of the voltage reference device 315 W-h'en the output signal or current from the full wave rectifier 326 which is a measure of the output voltage or the generator 210 is larger than the output signal or current .of

the other output terminal 367 of the minimum excitation limit circuit 310. The second control windings 314, 316, 318, and 320 are so disposed on their respective magnetic core members 250, 252, 254 and 256 that when current flows therethrough, the magnetomotive force or ampereturns produced thereby in the respective magnetic core members either opposes or is additive with respect to the ampere-turns or magnetomotive force produced by the current flow through the respective load windings 258, 260', 262, and 264 depending upon the direction of the output limit signal or current from the minimum excitation limit circuit 310 which appears at the output terminals 365 and 367 of said limit circuit.

In order to render the magnetic amplifier 240 responsive to only the algebraically larger of the output signals from the error detecting circuit 350 and the minimum excitation limit 310, an auctioneering circuit 390 is provided which includes the first control windings 330, 332,334, 336, the second control windings 314, 316, 318

and-320 and the thirdcontrol winding 302, 304, 306 and 308lof the magnetic amplifier 240, the full wave ,rectifier 362 and the resistor 356.- The lower input terminal .of the full wave rectifier 362 is connected to the output terminal 346 of the error detecting circuit 350 and to the output terminal 367 of the minimum excitation limit circuit 310, as previously mentioned. The first control winding,330, 332, 334 and 336 and the second control windings 3l4, 316, 318 and 320 of the magnetic amplifier 240 'jareconnected in series circuit relationship with each other between the output terminal 347 of the error detecting circuit 350. and the output terminal 365 of the minimum excitation limit circuit 310 through the resistor 352 with the common terminal between said first and second control windings being connected to the upper input windings 302, 304,306 a'nd308 are disposed in inductive relationship with the magnetic core members 250, 252, 254 and 256, respectively. 'rentwhich flows in the third control windings 302, 304,

During operation, the cur- 306 and 308 of the magnetic amplifier 240 is the difierence "the voltage reference device'315fthe 'direetiombf'the"75'betwcen"the""error signal 'or'cutrent from the errorde- When the output signal or current. from-the full wave rectifier 326 is less than the output,

' and "256' that when current 'flows therethrou'ghj the mag-3' netom'ot iv'e forceon ampere turnsriproduceduthereby inthe m'agnet-ic core members 25fi 'randii252, respectively; is additive with respect touthe ampere-turns ori'ama gnetoa motiveforce produced by the currentzflow through zthe; respective load windings 1258Yand 260- and the magneto:

- motiveforce or--ampere-turnsproduced thereby in the magnetic core members 25r4an'd 1256,:respectively; op-.; posesl the magnetomotive force or=i-ampere-turns =produced by--the currentdlow through-the respective load wind-i i'ngs 262'and'264; v i -tv -"--ilSimilarly to the output of the magnetic amplifier 60 as previously described in detail; Hthe net -or total output ofthe magnetic amplifier 240 aas measured byrthewrelae -tiv'e outputs of the sections 242 and 244m the buck and boost field windings 228 and 226, respectivelm'n'varies with only the algebraically larger of the control signals or currents from the errordetecting circuit 350 anda'the minimum-excitationlimitlcircuit"' 3 10.-It will be as;

V 12 the output current from theffull wave rectifier 326 and thus v inszaocordanc f with: the output volt-age Of: the-ageing; eratorr210= wThe vector 45,0 is gthe yect r difference tween the -vectors 430gand 440: and thereforenrepresents the net error signal or current which flows in the plifier 240.? Similarly to t the. vectorv 440;; the magnitude ofethe vector 450 varies with the; output voltage oft-the; ge'i'leratorr210v and direction of the vector ASOmay-reverse; during-operation when theoutput'voltage ofthe generator 7 output voltage. t Thenorrnal operatingpoint of. theiregulatorsystem 230, as indicated at 420 in FIGS, 4-,ata which the outputflvoltage of the generator 210 ismaintained; at substantially the regulated value can therefore be arranged to correspond to a -pa'rticular error signalor currentrtas,

indicated by the vector 450. The vector 460 represents the output limit signal from the excitation @limit circuit 310 during normal operating conditions when the errorsig'nal, as indicated by the vector 450, is algebraically larger or more positive than the limit signal, as indicated sumed" as a reference'direction thati the directiom-zofxa control signal or current is :positivev when n rrower 'said control signal or current in'theassociated controlnwindai ings ofthemagnetic amplifier: 240::tend's to increase the r 7 output 'ofthe section 242-and tends to decrease 'thevouts put of the section 244. 'In other words,w 'tlre net orttotal the'errordetecting circuit 350 and the minimum: excita= tion limitcircuit 310' with respect to the assumed referencefdirection. Forexample, the direction ofthe error signal or current'whose flowin the first control windings 330,;332 -334-and 336 of the magnetic amplifier 240: produc'es'=lthe magnetomotive'forces indicated by -the' solid arrowslin FIG.- 3 will-be considered positive while the direction of'the error signal or current whose fiow in'said first controlwindings produces the magnetor'notive forces indicated by the dotted'arrows in FlGs-3 'will be considered negative.

i-Referring to FIG. 4, the operation of the regulator loop or system 230 described-duringnormal operating conditions when the output error signal from 1 the error detecting circuit 350 is algebraically'larg'er orunore positi've than the output limit signal the minimum excitation limit circuit 310,]and-"said:regulator system -is responding only to 'saidjerrorsignahf In p arti'c'ular," there is'shown in FIG. 4' a transfer characteristiccurve410for inwhich the net averageioutpu-tiof the magnetic amplifier .2401Whi'cl1 is applied to the buck and boost field windings 2'28 and 226, respectively5gof. the WeXciten-ZZU rvarie's'with changes in the magnitude of the" net controli'ampe're-turns as produced by'the current flow through the first; second andthi rd control windings of said m'agneticgarnplifier. In FIG. 4, a vector 430 represents the control ampere-turns produced'by the output current from the'vol'ta'gerefer'ence device 315 flowing through the first controlfwindings 330, 337; 334 and 336 ofthetmagnetic amplifier'240; ,l Since the effective currentflow through the:first control ingsQZtO-thmugh-SGG of the magnetic amplifier 240 =fr0m plifiertg ttl-whenthe output voltage of the generator210 V ismsubstantiallyat, thepredetermined --regulatedhyalue.

, Qlfhe magnitude ofuhe vector 44h accordance with output voltage of the regulated value. 1 45 7 by the vector 460, and when the regulator -system 230 is responding only to the error signal from the error detecti t i i 350 t. I r 1 vi: 1.; 'tIJJ; -During1the normal operation of the regulator system 230 when said regulator system is responding only to the error-signal the error detecting circuit 350and the output voltage of the generator 210 increases to a v'alue above its regulatedvalue, the current flow from the error detecting circuit 350 through the fir men-nor windings v 330'throu 336 of th ma eti" am lifier-240 d a output or" the'magnetieamplifier 240- varies with onlyathe, gh e gn c p are Ses moreipositive or less negative of the control signalsdrom or reverses and then increases. in the -'opposite direction to therebydecreasethe output current'froma the section 242 ofthe; amplifier 2'40 and increase the outputcurrent I a from'the' section 244 of the'push' -pull magnetic-amplifier 240: Such an action increases thecurrent flow through the buck field winding 226 'of the exciter 22(Vand decreasesthecurrentiflow through the boost fieldwinding 2 228" to thereby decrease the-output voltage of the exciter 220. "Adecrease inthe output'voltage of theexciter'220 'decr'easesthe magnitude ofthe' voltage across the field winding212 of the generator 210 totherebymeturn"the generator 210 to its predetermined .Qn the" other hand, a decreasein the output voltage of :thegenerator 210ito a value below its regulatedwaluejincreasesithejmagnitude of the netleurren-t flowtrorn the error detecting circtut'GSWthrough the first control windfingjs 330 through 336 olfthejmagnetic -a'rr1plifierf240 in a direction which is positive withfrespect 'to the assumed reference direction An. increase ginthe' current flow through the first control winding 330 through 336. of the magneticamplifier240m the latter direction unbalances 4 "rnagnetictamplifierin such a direction that the output current from the section 242 of said amplifiers increases and the output icurrent from the. section 244 decreases. Such "an'action' increases the magnitude of the current flow' throughthe boost field winding 228 of the ,exciter '220 and decreases the. magnitude of the current flow from the'bucl; field winding-226.- i This; in turn, increases; the magnitude of the output voltage of the exciter 220 asfiwell as the magnitude of the voltage across the field, winding 2121 of the exciter 210 to thereby return the magnitude ofjthe output voltage of the generator 21th 'tosubstantially its regulated values a v f I I I, The minimum excitation limit circuit .310 is of the same general type which is disclosediin Us. Patent. 12362412 which=.was --issued on an application of I T. Carleton et ing 'inputfarid output terminals; aninpedaneecircuit 331 connected, through the transformers i323. to -theuelectrical circuit, whichvincludes the conductors and t: y control windings; 330 through- 336' of; the: magnetic amrent flow through the line conductor 216.

aoomes 218, to be energized by a measure of the current'flowing in the electrical circuit and by a measure of the voltage in said electrical circuit; circuit means 333 connected to the impedance circuit 331 for applying to the input terminals of both. of. the rectifier units 394 and 396a voltage proportionalto the measure ofthe voltage in said electrical circuit, the measure of the voltage in said electrical circuit, including the conductors 214 and 218, that is applied to the rectifier 394- being of substantially greater magnitude thanthemeasure of the voltage in the electrical circuit that is applied to the rectifier 396, and for applying to the input terminals of the rectifier 396 a voltage proportional to the measure of the current flowing in the electrical circuit, which includes the. line conductors- 214, 216 and 218; and an electrical network 335 connected tothe output terminals of the rectifiers 394 and 396 for producing at its output a unidirectional or direct-current voltage that is a measure of the difference in the output voltages of the two rectifiers 394 and 396.

More specifically, theimpedance circuit 331 comprises the potential transformers 370 and 380 having the secondary windings 374 and 384, respectively, and the primary windings 372 and 382, respectively, connected to be responsive to the voltage across two phases of the three-phase electrical circuit which includes the line conductors214, 216 and 218; and an impedance member, more specifically a variable resistor 392, responsive to a measure of the current fiowing in the remaining phase of the three-phase electrical circuit, including the line conductors 214, 216 and 218. In order to obtain the proper magnitude of voltage across the primary windings 372and 382 of the transformers 37 0 and 380, respectively, the potential transformers 323 are interconnected between'the primary windings 372 and 382 of the transformers 370 and 380, respectively, and'the line conductors 214, 216 and 218L In like manner, in order to obtain "the proper magnitude of voltage across the variable resistor 392, a current transformer 342 is disposed to be responsive tothe magnitude of the current flow through" the line conductor 216. In order to, apply a voltage to "the input terminals of the rectifier-394 that is a measure "of the terminal voltageof the generator 210, the secondary winding 374 of the potential transformer 370 is connected to the input terminals of the rectifier 394.

On the other hand, in order to apply to the input terminals of the r'ectifier'396, a voltage proportional to the vector sum of the voltages across the variable resistor .392 and thesecohdary winding 384- of the potential transformer 380, the variable resistor 392 and the secondary winding 384 are connected in series circuit relationship with one another, the series circuit being connected to the input terminals of the rectifiers 396. The voltage across the secondary winding, 384 is likewise proportional to or vvaries with the terminal voltage of the generator210. ljThe voltage, however, across the secondary winding 374 the unidirectional or direct-current output voltage of said minimum excitation limit circuit.

During the operation of the minimum excitation limit circuit 310, as explained in greater detail in US. Patent 2,862,172, previously mentioned, the output limit signal which appears at the output terminals 365 and 367 of the minimum excitation limit circuit 310 and which is applied to the limit windings 314 through 320 of the magnetic amplifier 240 follows the pull-out characteristic of the generator 210. When the apparatus shown'in FIG. 3 is operating within the minimum excitation limit and the net voltage across the resistor sections 368A and 368B is of a polarity which is positive at the terminal 365 with respect to the voltage at the terminal 367, as indicated by the vector 460 in FIG. 4,.the regulator system 230 is responding only to the error signal from the error detecting circuit .350 and the minimum excitation circuit 310 has substantially no effect on the operation of said regulator system since the error signal from the error detecting circuit 350 is algebraically larger or more positive than the limit signal from the minimum excitation limit circuit 310. Assuming, however, that the system conditions change and the load on the generator 210 increases to the extent that the voltage across the resistor section 368B becomes greater in magnitude than the voltage acrossthe resistorfsection 368A, then the minimum ,exc'itation'circuit 310 will begin to afiect the operation of 368A and 36813 reverses and the direction of the output signal from the minimum excitation limit circuit 310 also reverses as indicated by the vector 470 in FIG. 4. As

soon as the output signal from the minimum excitation limit circuit becomes algebraically larger or more positive than the error signal from the error detecting circuit 350,.as indicated by the vectors 470 and450, respectively,

in FIG. 4, the regulator system 230 then becomes responsive only to the output limit signal from the minimum excitation limit circuit 310 during the latter operating condition. When the output signal from the limit circuit 310 becomes more positive than the output error signal from the error detecting circuit 350 and the output is always of substantially greater magnitude than the j 'voltage across the secondary winding 384 of the potential transformer 380.

The voltage across the variable resistor 392 variesin accordance with the magnitudeof the curf In this instance, the electrical network 335 comprises a 'potentiometerincluding two resistor sections 368A and 368B. The resistor section 368A is connected to the output terminals of the rectifier 394 and the resistor section 368B is connected'to the-output terminals of the rectifier 396, the resistor sections 368A and 368B being con- 1 nected in series circuit relationship with one another so that the net voltage across the, resistor sections 368A and 36813 is proportional to the'difference in the specific voltages appearing across each of said resistor sections.. A filtercircuit which, includes a linear filter reactor 366 and I a capacitor 364 is interconnected between the resistor sections 368A and 3683 and the output terminals 365 and 367 of the minimum excitation circuit 310 for smoothing limit signal is positive at the output terminal 367 with re spect to the voltage at the output terminal 365, then current flows from left to right through the second control or net windings 314 through 320 of the magnetic famplifier240 thus producing the magnetomotive forces as indicated by the solid arrows in FIG. 3. Since thenet sum or total of the control ampere-turns of the magnetic amplifier 240 is responsive only to the output limit signal from the limiting circuit 310 during the latter assumed operating condition, the outputof the section 242 of the amplifier 240 is increased and the output of the section 244 'is' decreased. This increases the magnitude of the current flow through the boost field winding 228 of the ,exciter 220 and decreases the magnitude of the current 1 flow through the buck field winding 226. With such an increase in the magnitude of the current flow through the boost field winding 228, the output voltage of the exciter 220 is increased to increase the magnitude of the current flow to the field Winding 212 of the generator 210 and thereby prevent the generator 210 from falling out of step or synchronism. The dotted arrows adjacent to lthe direction of the magnetomotive forces produced in the second control-or limit windings 314 to 320 indicate the respective magnetic core members by the current flow through said second control windings when the apparatus shown in FIG.-3 is operating within the minimum excitation limit. It is to be noted that the minimum excitation limit disclosed in US. Patent No. 2,862,172, previously mentioned, may be modified to provide either a static minimum excitation limit or a dynamic minimum excitation limit.

, said-.,input. control, signals. v,

- 1s tion has several advantages. "For example, the output of an auctioneering circuit .ascdisclosed isresponsive onlvto the algebraically larger or smaller-of tw ojin'put control .signalsvor currents regardlessofrwhether oneor both of said control signals reverses indirection or inpolarity.

- In addition, several auctioneering circuitsof the type-disclosedmay be cascaded to obtain. an output which varies only with the largestof a pluralityofinput control signalsgreater than two.

sinceinurnerous changes maybe made in the above describedapparatusandcircuits and different embodiments of the invention may bemade withoutdeparting fro'in the spirit and scope thereof, it is intended that. all the mattercontainedin the1 foregoing descriptionsor shown in I the accompanyingdrawing shall beinterpreted as illustrativeand not in a limiting sense. We claim-as our invention:

output winding, said first and second control windings being responsive to first and secondinput control signals,

respectively,. .the turns of eachof-said control windings being substantially equal, and'reotifier means connected in circuit relation with said third controlz windi-ng ;ifof rendering said. third control winding responsive to the I magnitude of the difference between said first 'and' sec L In combinatioma magnetic amplifier having control windings responsive to the sumvoffirst and second input signals and anfladditional control winding, and means connected in circuit relation withjsaid additional control windingv for. applying the magnitude of thei'diilerence between said inputsignals thereto, theoutput of, said saidinputsignalsr v 12 v I z 2. In combination a magnetic amplifier having control windings responsive to the sum of first and second input signals and-an additional control winding, and rectimagneticamplifieribeing responsive only to the larger of fiermeans'connected in circuit relation with said additional control. winding for applying the magnitude of the [difference between saidinput sig'nalsthereto, the output of said magnetic amplifier being responsiveonly to the larger of saidinputsignals. V It H 3. Iii-combination, 'a'magnetic amplifier having controlwindings responsive to the sum of first and second input signals and anladditional control winding, the turns 7 of said additional .i control, winding being substantially equal-to those ofeach of-the first-mentioned control .windings, and rectifier means connected in circuit. relation with said additional controlwinding for applying the mag- .nitudeof the dififerencebetween said input'isignalsthereto, the output of saidmagnetic amplifier being.responsive only, to the larger ofsaid ,inputnsignals. v I

4. In an electric control apparatus,..a magnetic amplifier having first, second and !third control windings and an output winding,'.said first and second, control windings being responsive to first andsecond 'inputcontrol signals, trespectively, and means connected in circuittrelati on with said third controlwindingfor rendering said third controlwinding responsive .to the, magnitude .ofthe difference the sum of the input signals applied-thereto,firstmeans foriapplying a-first input signal to said amplifying means, second-means for applyinga second input signal to said between said-first and second control,,Signals, the;output of;said magnetic amplifienvar'ying only. .w ith the iarger of 5,. In an electric control apparatus, a magnetic ainplifier having first, second. and third-control windings and a n'output winding, said firstand second control windings;

being, responsive. to first and. second input control signals,

respectively, and means connected in circuit relation ;'with' saidthird, control winding for, rendering said third 3 control winding responsive, to the magnitude ,of 'the difference Si a s t e slap?- a dp fi ryary nagn y w th the-Sm 9 between said first andseeond, cont saidinput controlsignals. i

,6; In.a n electric control apparatus, a magnetic ampli- .Il:?l. --I1r1an electric control apparatus ai magnetic amplifier having first, second and third control windings-,andgan between said first; means and saidifieldfwinding for. app

signals.

. nieansefor, obtaining an error signalgwhich v es theh-deviationlofi said output .voltag o nd cont'r'olsignals, the output of said'outputwinding of said magnetic amplifier varying onlyfw'ith' the larger-of Y 8. In an electric control apparatus, anragnetic'ampli fier having first,]second and third control-windings and anoutput winding, said firstand-second control windings being responsive to first and second input controlesignals, respectively, and means connected in circuitrelation-with said third control winding for rendering said third con-trol winding responsive to the magnitude of the difference between said first and second control currents, theoutput of said, output winding of said magneticamplifier'varying only with the larger-of said input control currents. H

9,111 an electrical control apparatus, the combination comprising, amplifying means magnetically responsive to amplifying means, and third means for electrically applying the difference between first andsecond inputsignals as-a tllird input signal to said amplifying means the larger'of said first and secondiinput signals.

output of said amplifying means varyingwithonly the v 3 10.; In an elect-r'ical control appanatusthe combination comprising, amplifying means responsive to the sum of the input currents applied thereto, .first means for applying a first input current to saids..amplifying means, second means for applying a second inputcurrent to,said

'amplifyi-ngmeans, and third. means for, applying the difierence -betwen first and second input curren sgas a third'inputcurrent tosaid amplifyingmeans, theputput of said'amplifying means,'-'varying with,. onl y the larger of said firstand secondinput currents.

x 11. "In -an electrical control apparatus, the teatimtioncomprising, amplifying means, responsive to the of the -unidirectional input signals applied thereto, first means for applying a firstnnidirectionalinput signal to 1 said amplifying .meanalsecond; means for pappiy' -second...unidirectional- ,input signal to; said means, and third means for applyingthe difference f be-' tween first. and; second unidirectional input; signals; asga third unidirectional input signal tqsaid an plifyingnieans, the .output of said amplifying means varyin with onl the larger of said. first and second unidirect 12.. In a regulator system for maintaining the output voltageof a dynamoelectric machine having oyitputtermk n'als and; an excitation field winding. at, subst nti all predetermined value, the combinatio' i mined ;va111e,1 second means .connec edfin c rcuit trolling the. el citation current suppIied thereto n accordance with the. net of the signals applied to said second means, third means connected n, circuit relatien between saidputput terminalsand said second means g .a limiting signal thereto during "certain operatingico'nditions, and fourth meansconnected incircuit I relation withl said second meansfor appl ying 'thereto the difference 7 between said error signal and-said limiting signal, the output of said second meansvaryingonlywith the larger of" said error andilimiting lsignalsi 7 a regulatorssystem for, maintaining the output voltage Ora dynamoelectri a hi h ying,oufi1 m@Um' nals and: an excitation; field;,w;ind ing t. Substantially a 4 means 1 for;-.. obtaining an em -or signal whic predetermined value, ,the combination; ompri'sing fir eviationgof saidputput voltage from said said input. control signals. 7

termined value, magnetic amplifier means connected in thereto in accordance with the not sum of the control signals applied to said magnetic amplifier means, second a means connected in circuit relation between said output terminals and said magnetic amplifier means for applying a limiting Signal thereto during certain operating conditions, and third means connectedin circuit relation with said magnetic amplifier means for applying thereto the difierence between said error signal and said lim ting signal, the output of said magnetic amplifier meansvarying only with the larger of said error and limiting signals,

14. In a regulator system for maintaining the output voltage of a dynamoelectric machine having output terminals and an excitation field winding at substantially a predetermined'value, the combination comprising, first means for obtaining an error signal which varies with the deviation of said output voltage from said predetermined value, second means connected in circuit relation between said first means and said field winding for controlling the excitation current supplied thereto substantially in accordance with the net sum of the signals applied to said second means, third means connected in circuit relation between said output terminals and said second means for applying a limiting signal thereto during certain operatingconditions, and rectifier means connected in circuit relation with said second means for applying thereto the difference between said error signal and said limiting signal, the output of said second means varying only with the larger of said error and limiting signals.

15. In a regulator system for maintaining the output voltage of a dynamoelectric machine having output terminals and an excitation field winding at substantially a "predetermined value, the combination comprising, first means for obtaining an error signal which varies with the deviation of said output voltage from said predetermined value, magnetic amplifier means connected in circuit relation between said first means and said field winding for controlling the excitation current supplied there-' applying thereto the difference between said error signal and said limiting signal, the output of said magnetic amplifier means varying only with the larger of said error and limiting signals.

16. In a regulator system for maintaining the output voltage of a dynamoelectric machine having output terminals and an excitation field winding at substantially a predetermined value, the combination comprising, first means for obtaining an error control current which varies with the deviation of said output voltage from said predetermined value, second means connected in circuit relation between said first means and said field winding for controlling the excitation current supplied thereto in accordance with the sum of the control currents applied to said second means, third means connected in circuit relation between said output terminals and said second means for applying a limiting control current thereto during certain operating conditions, and fourth means connected in'circuit relation with said second means for applying thereto the difference between said error control current and said limiting control current, the output of said second means varying only with the larger of said error and limiting currents. I

17. In a regulator system for maintaining the output voltage of a dynamoelectric machine having output terminals and an excitation field winding at substantially a predetermined value, the combination comprising, first means for obtaining an error control current which varies with the deviation of said output voltage from said predetermined value, magnetic amplifier means connected in circuit relation between said first means and said field Winding for controlling the excitation current supplied thereto in accordance with the net sum of the control currents applied to said magnetic amplifier means, third means connected in circuit relation between said output magnetic amplifier means varying only with the larger of said error and limiting control currents.-

18. In a regulator system for maintaining the output I voltage of a dynamoelectric machine having output terminals and an excitation field winding at substantially a predetermined value, the combination comprising, first means for obtaining an error signal whichvaries with the deviation of said output voltage from said predetermined value, amplifying means connected in circuit relation between said first means and said field winding for controlling the excitation current supplied thereto in accordance with the net sum of the signals applied to said amplifying means, second means connected in circuit relation between said output terminals and said amplifying means for applying a limiting signal thereto during certain operating conditions, and third means connected in circuit relation with said amplifying means for applying thereto the difierence between said error signal and said limiting signal, the output of said amplifying means varying only with the larger of said error and limiting signals.

19. In a regulator system for maintaining the output voltage of a dynamoelectric machine having output terminals and an excitation field winding at substantially a predetermined value, the combination comprising, first means for obtaining an error signal which varies with the deviation of said output voltage from said predetermined value, magnetic amplifier means having control windings connected in circuit relation between said first means and said field winding for controlling the excitation current supplied thereto in accordance with the signals applied to said control windings, second means connected in circuit relation with said output terminals for obtaining a limiting signal, the sum of said error and limiting signals being applied to certain of said control windings, and third means connected in circuit relation with another of said control windings for applying thereto the difference between said error and limiting signals, the output of said magnetic amplifier means varying with the larger of said error and limiting signals.

20. In a regulator system for maintaining the output voltage of a dynamoelectric machine having output terminals and an excitation field winding at substantially a predetermined value, the combination comprising, first means for obtaining an error signal which varies with the deviation of said output voltage from said predetermined value, magnetic amplifier means having a plurality of control windings connected in circuit relation between said first means and said field winding for controlling the excitation current supplied thereto in accordance with the signals applied to said control windings, second means connected in circuit relation with said output terminals for'obtaining a limiting signal, the sum of said error and limiting signals being applied to certain of said control windings, and rectifier means connected in circuit relation with another of said control windings for applying thereto the difierence between said error and limiting signals, the output of said magnetic amplifier means varying with the larger of said error and limiting signals;

21. In a regulator system for maintaining the output voltage of a dynamoeleotric machine having output terminals and an excitation field winding at substantially a predetermined value, the combination comprising, first means for obtaining an error signal which varies with the thi cdntrpl windings connected;,in ,circuitrelation. be tween. fixst-means and said field Winding for con-u trolling {the excitation current. supplied theroto iinwaccord;

qse l-w n h s ns iap li -s -m1- in secqndineans connectcd in' circuiL relation with said Qutpl tje 'minals foiapbtaining a limiting: sign a1, said senior amass anti niting signals beingappliedto said first and seco'nd-q con 1 wind ings respectively, and third means, connected in clgit pelationwith said..thind coiitml Winding for applyingttheretqtthe difference .betweenv said .erroi and i limiting signals, the. output 40f .said magnetic amplifier;

mqansH-vaa yingwith only the largei ofisaiderror and i 'as a r -y V. i s.

22,;- In a iegulator system i for imaint aining l the output j qt qfi d am e s i mach e having pums mipals and an excitation field winding atsubstantiallya predetermined value, the combination. comprising first onil atndlthigd 'contrqi windings connectcdin circuit rela A tiontbetween saidilfimt meansand saidtfieid rwindinggforn.

signalmwhichi vanies wim t the 15i vi- 9 "ngrsaid gntpi t vdltagqtffomisaid pl edetersg mine a1uc,1- magnetiq:ampiifierrmeans.having-;first,- sec connected, in cincui tu relation... witlielsai d third lcontroly}.

winding;,-fo r:applyinggtheretoithe idifieyence :between :said'. errant and zlimiting signa1s,' the :output: ro fh said magnetic amplifiersmeanswamyring with1on1? the largeiz of said error? and limiting si-gnats. 1 7 

